1. Field of the Invention
The present invention relates to an optical tomographic imaging apparatus and an optical probe, and in particular, to an optical tomographic imaging apparatus and an optical probe capable of stabilizing the light intensity of a returning light beam received by measurement optics such as an optical fiber which outputs a measurement light beam.
2. Description of the Related Art
Conventionally, there are known optical tomographic imaging apparatuses utilizing optical coherence tomography (OCT) measurement as a method of acquiring a tomographic image without dissecting a measurement object such as living tissue.
OCT measurement is an optical interferometric measurement method in which a light beam outputted from a light source is divided into two light beams, namely, a measurement light beam and a reference light beam, and which utilizes the fact that optical interference is only detected when respective optical path lengths of the measurement light beam and the reference light beam become consistent with each other within the range of a coherence length of the light source.
In addition, the measurement light beam is to be guided by an optical probe to a measurement object, and a returning light beam from the measurement object is to be also guided by the same optical probe. In such an optical probe, a transmitting surface capable of transmitting a measurement light beam or a returning light beam is formed on a portion of a probe outer casing of the optical probe. A light beam outputted from an optical fiber inside the optical probe passes through an optical system such as a lens or a prism and is then transmitted through the transmitting surface of the probe outer casing to be irradiated on the measurement object as a measurement light beam.
With respect to such an optical tomographic imaging apparatus, Japanese Patent Application Laid-Open No. 2003-028791 discloses a technique in which, for each different optical probe, optical path lengths of a reference light beam and a measurement light beam are adjusted so that the optical path lengths become approximately consistent with each other.
In addition, U.S. Pat. No. 7,158,234 discloses a technique for detecting a reflected light beam from an optical window that is a transmitting surface of a probe outer casing to adjust a focal point of a probe light beam and an optical path length difference between a reference light beam and a measurement light beam.
Furthermore, U.S. Pat. No. 6,564,089 and Japanese Patent Application Laid-Open No. 2004-223269 disclose techniques in which a light beam is obliquely outputted with respect to a transparent cover (sheath) covering an outermost surface of a catheter in order to reduce the intensity of a reflected light beam reflected off of the cover surface and to prevent multiple reflection ghosts from being generated in a measurement image.